1. Field of the Invention
The present disclosure generally relates to patient monitoring devices and more specifically, embodiments of the present disclosure relate to driving light sources of patient monitoring devices to properly irradiate tissue under observation.
2. Description of the Related Art
Spectroscopic patient monitoring systems including noninvasive patient monitoring systems often energize a plurality of emission devices that irradiate tissue under observation. In many systems, the emission devices irradiate the tissue at different wavelengths at different times. The radiation is scattered and absorbed by the tissue such that some attenuated amount thereof emerges and is generally detected through one or more photodetectors. The photodetectors output one or more signals indicative of the intensity of the detected attenuated radiation and forward the signal to a patient monitor for processing.
In many systems, the patient monitor provides a drive signal configured to activate each emission device at a different time over an activation cycle, thereby reducing a likelihood that a detector seeking a measure of attenuation in light of one wavelength will be effected by radiation from light of another wavelength.
For example, FIG. 1 illustrates a patient monitoring system 100 including a patient monitor 102 communicating with a noninvasive optical sensor 104 through cable 106. As shown in FIG. 1, the monitor 102 displays calculated measurements derived at least in part from processing an output signal from the sensor 104 indicative of light attenuated by pulsing blood. As shown in FIG. 1, the monitor 102 includes a driving circuit 108 configured to drive a sensor light source 110, such as, for example, a two emitter light source configured to emit light at different wavelengths. The emitters shown in FIG. 1 are connected in parallel in a back-to-back configuration, although other configurations and their drive circuitry requirements will be recognizable to an artisan from the disclosure herein, including, for example, common anode, common cathode and the like.
In general, a processor of said monitor 102 controls various latching mechanisms to activate one of voltage-to-current converters 112, 114 at a time. Once activated, the converters 112, 114 provide a current through conductors of the cable 106 to an associated LED 116, 118 of the sensor 104. Thus, the processor may output appropriate latching signals to the driving circuit 108 to precisely control a duty cycle and current level for each of the LEDs 116, 118, and ensure that the LEDs 116, 118 are activated one at a time. Examples of the driver circuitry of FIG. 1 are disclosed in U.S. Pat. No. 6,157,850. The '850 patent disclosure is incorporated in its entirety by reference herein.
In contrast to the driving circuit 108 and light source 110 of FIG. 1, FIG. 2 illustrates a patient monitoring system 200 including a patient monitor 202 communicating with a noninvasive optical sensor 204 through a cable 206. As shown in FIG. 2, the monitor 202 displays calculated measurements derived at least in part from processing an output signal from the sensor 204 indicative of light attenuated by pulsing blood. As shown in FIG. 2, the monitor 202 includes a driving circuit 208 configured to drive a sensor light source 210, such as, a grid array of LEDs capable of emitting light at different wavelengths of radiation.
In general, the driving circuit 208 includes a plurality of row drivers 220 and a plurality of column drivers 222, the activation of a particular row driver and a particular column driver corresponds to the activation of one or a group of LEDs arranged at a corresponding node in a grid of rows 224 and columns 226. Such activation is controlled through one or more processors of said monitor 202 in order to precisely control a duty cycle for each of the LEDs in the grid array, including LEDs 216, 218. For example, row and column drivers 220, 222 function together as switches to Vcc and current sinks, respectively, to activate LEDs and function as switches to ground and Vcc, respectively, to deactivate LEDs. This push-pull drive configuration advantageously prevents parasitic current flow, and thus, parasitic activation, in deactivated LEDs. In a particular embodiment, one row drive line 224 is switched to Vcc at a time. Examples of the driver circuitry of FIG. 2 are disclosed in U.S. pat. app. Pub. No. 2006/0241363. The '363 patent application's disclosure is incorporated by reference in its entirety herein.